This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 10-268301, filed Sep. 22, 1998, the entire contents of which are incorporated herein by reference.
The present invention relates to a method and apparatus for aligning a target object such as a semiconductor wafer.
A wafer inspection apparatus for detecting, for example, defects in semiconductor wafers adjusts, before inspection, the position of the center of each wafer placed on a mount table for inspection.
There is a conventional wafer inspection apparatus of this type, in which while an edge of a wafer placed on a mount table is pushed by centering means such as a pin, or while the wafer edge is held by chuck means, the wafer is moved toward the axis of rotation of the mount table to align the center of the wafer with the axis of rotation of the table, thereby detecting wafer""s orientation flat or notch on the basis of an output from a photoelectric sensor including a light emitting unit and a light receiving unit that are arranged such that a portion of the edge of a rotating wafer crosses their optical axis, and positioning the wafer such that the detected orientation flat or notch will be situated in a predetermined position.
However, where the centering means or chuck means that contacts an edge portion of a wafer is used, there is a probability that the wafer will be damaged by a shock applied thereto or contaminated as a result of being rubbed by the mount table. Furthermore, the photoelectric sensor, which is formed of the light emitting unit and the light receiving unit arranged such that an edge portion of each wafer crosses their optical axis, is provided as a unit dedicated to detect the orientation flat or the notch of each wafer. Therefore, the structure of the entire apparatus is inevitably complicated, and hence is very expensive.
Accordingly, it is an object of the present invention to provide a method and apparatus for aligning a target object, that can detect the center of a target object such as a wafer, without touching the wafer and which can be manufactured to be compact and at low cost.
According to one aspect of the invention, there is provided an apparatus for aligning a target object, comprising: an objective lens for magnifying an image of the target object; focusing means including a laser source for irradiating the target object through the objective lens and a focus detecting light-receiving section for receiving light reflected from the target object, the focusing means being used for detecting a defocus from a detection result of the focus detecting light-receiving section to execute focusing; displacing means for changing a relative positional relationship between the target object and the objective lens such that a laser beam is emitted from the laser source of the focusing means to at least three points of a periphery of the target object; edge detecting means for detecting edge positions corresponding to at least three points excluding an orientation flat or a notch in the periphery of the target object, using the laser beam emitted from the laser source of the focusing means; and operating means for calculating a central position of the target object based on the edge positions detected by the edge detecting means.
The apparatus may further comprise control means for positioning the target object based on a result of the operating means.
In the apparatus, the edge detecting means may include a receiving section, provided on a different side of the target object from the objective lens and close to the periphery of the target object, for receiving light passing the target object.
In the apparatus, the receiving section may include a condenser lens for condensing the laser beam emitted from the objective lens and a photodiode for outputting an electric signal corresponding to an amount of the condensed laser beam.
In the apparatus, the edge detecting means may include a receiving section for receiving light reflected by the target object via the objective lens.
In the apparatus, the edge detecting means may detect an edge based on a variation of amounts of light in the focus detecting light-receiving section of the focusing means.
The apparatus may further comprise selecting means for selectively validating a function of the edge detecting section and invalidating a focusing function of the focusing means.
In the apparatus, the focusing means may be an autofocus unit into which the laser source and the focus detecting light-receiving section are integrally incorporated as one component.
In the apparatus, the focus detecting light-receiving means of the focusing means may include a plurality of light-receiving elements, and the edge detecting means may detect an edge based on a value obtained by adding signals generated from the plurality of light-receiving elements.
In the apparatus, the plurality of light-receiving elements may be used in detecting a focal point according to a confocal method.
In the apparatus, the plurality of light-receiving elements may be used in detecting a focal point according to a pupil split method.
In the apparatus, the plurality of light-receiving elements may be used in detecting a focal point according to an astigmatism method.
According to another aspect of the present invention, there is provided a method of aligning a target object applied to an optical device having an objective lens for magnifying an image of the target object, the method comprising the steps of: stopping a focusing function of an autofocus unit; irradiating the target object with a laser beam from a laser source provided in the autofocus unit through the objective lens while varying a relative positional relationship between the target object and the objective lens; detecting edge positions corresponding to at least three points excluding an orientation flat or a notch in a periphery of the target object, based on a variation of amounts of light reflected from the target object in a focus detecting light-receiving section provided in the autofocus unit; calculating a central position of the target object based on the detected edge portions; and positioning the target object based on the calculated central position.
In the method, in the edge position detecting step, an edge may be detected based on a value obtained by adding signals generated from a plurality of light-receiving elements constituting the focus detecting light-receiving section.
In the method, the autofocus unit may detect a focal point according to a confocal method.
In the method, the autofocus unit may detect a focal point according to a pupil split method.
In the method, the autofocus unit may detect a focal point according to an astigmatism method.
In the method, in the central position calculating step, coordinates of the central position may be acquired using a formula for a circle.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.